The renal molecular clock: broken by aging and restored by exercise.

The mammalian circadian clock governs physiological, endocrine, and metabolic responses coordinated in a 24-h rhythmic pattern by the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. The SCN also dictates circadian rhythms in peripheral tissues like the kidney. The kidney has several important physiological functions, including removing waste and filtering the blood and regulating fluid volume, blood osmolarity, blood pressure, and Ca2+ metabolism, all of which are under tight control of the molecular/circadian clock. Normal aging has a profound influence on renal function, central and peripheral circadian rhythms, and the sleep-wake cycle. Disrupted circadian rhythms in the kidney as a result of increased age likely contribute to adverse health outcomes such as nocturia, hypertension, and increased risk for stroke, cardiovascular disease, and end organ failure. Regular physical activity improves circadian misalignment in both young and old mammals, although the precise mechanisms for this protection remain poorly described. Recent advances in the heart and skeletal muscle literature suggest that regular endurance exercise entrains peripheral clocks, and we propose that similar beneficial adaptations occur in the kidney through regulation of renal blood flow and fluid balance.